The second half of the last century produced a staggering wealth of information about the cellular and molecular processes of life. The quantity and quality of this data is ushering in a new mode of thinking in the biomedical sciences that relies heavily on mathematical and computational tools and on rigorous quantitative experimental methods. With increasing frequency, these analytical tools and experimental methods are not home grown within the life sciences, but are adopted from research in the physical and mathematical sciences. This brave new world requires a new kind of researcher, one who easily moves between the bench and the workstation, one who is equally at ease with running microscopes as with running simulations, and one for whom building quantitative models and testing them by designing equally quantitative experiments comes naturally. The Quantitative Biology (QB) Program at Brandeis University brings together six different Ph.D. programs from five science departments in order to train students who can rise to this interdisciplinary challenge. QB is an official interdepartmental graduate program at Brandeis that has just completed its seventh full academic year of operation; the program currently has 50 enrolled students and is the largest graduate program in the sciences at Brandeis. QB leverages the strengths of existing disciplinary Ph.D. programs at Brandeis by bringing together students from these programs in a specialized curriculum that is designed to take advantage of the learning opportunities afforded by training in multi-disciplinary groups. Students admitted to graduate study in the Biochemistry & Biophysics, Chemistry, Computer Science, Molecular & Cellular Biology, Neuroscience, or Physics Ph.D. programs who choose the QB track, receive upon successful completion a Ph.D. degree in their chosen discipline with an additional specialization in Quantitative Biology. This approach provides the students with modern discipline-bridging training while providing the graduate with a Ph.D. credential that has proven value on the job market because it is in a recognized traditional discipline. Students typically enter the QB program in either the first or second years of their Ph.D. studies and remain affiliated with QB until they graduate. Each student selected for support by the training grant is supported either in years one and two, or two and three, so as to achieve the best fit between QB training and the course of study in the student's home Ph.D. program.